Actuator for diaphragm type switch



June 23, 1970 J. 1.. YARBOROUGH 3,517,149

ACTUATOR FOR DIAPHRAGM TYPE SWITCH Filed Oct. 15. 1968 I N VEN TOR. JAMES L. YARBOROUGH BY 'Q WCFWM/ ATTORNEY United States Patent ACTUATOR FOR DIAPHRAGM TYPE SWITCH James Lowell Yarborough, Raleigh, N.C., assignor to International Business Machines Corporation,

Armonk, N.Y., a corporation of New York Filed Oct. 15, 1968, Ser. No. 767,755

Int. Cl. H0lh 3/02 US. Cl. 200-172 3 Claims ABSTRACT OF THE DISCLOSURE A diaphragm switch of the type having a flexible conductor pressable through a perforation in an insulator into contact with a fixed lower conductor will normally be actuated by a dimple formed on a driven member. To prevent damage to the flexible conductor, the dimple is moved to contact closing position relatively slowly to diminize dynamic forces and is in the form of a bead of rubberlike material shaped to avoid concentration of stress in the conductor. The switch actuating force appl ed through the dimple is controlled by mounting the dimple on a low rate spring as the driven member and by limiting the stroke of the driving member.

Background of the invention Elastic diaphragm switches are now being developed for inexpensive, low current applications involving a plurality of circuits, se e the assignees US. Pat. No. 3,308,253 issued Mar. 7, 1967 to M. Krakinowski. One example of such an application would be in a keyboard of the alpha-numeric type for a data transmission terminal wherein semi-conductor control circuits are selectively closed by operation of the keys. The diaphragm switch will comprise a substrate having printed circuit wiring forming one set of switch contacts, an insulating film of Mylar or the like with perforations at the contact points of the substrate and an overlayer of an elastic diaphragm havin conductors bonded thereto. These conductors will normally be spaced from those on the substrate by the insulating film but can be depressed through the perforations to make the required contact. In the keyboard noted above, the switch actuator was originally a metallic dimple formed on a cantilever spring which was retained in deflected position by an interposer under its end. Operation of a key of the keyboard acted to withdraw the interposer past the end of the spring and allowed the spring to snap into an active position wherein its dimple pressing against an elastomeric top protective sheet, closed the switch contacts and with its free end latched the interposer against return. A mechanical machine cycle then moved the interposer below and under the end of the spring then returned the interposer and spring to the normal deflected position. It was found that the fast snap action of the spring needed for latching the interposer in the set position generated a dynamic force such that the diaphragm and its conductors were subject to rupture by the dimple as the switch was closed.

Description of the invention This invention relates to an actuator for a switch and more particularly to an actuator which will transmit only a controlled force through a compressible element to an elastic diaphragm type of switch.

It is an object of this invention to provide an actuator for an elastic diaphragm type of switch, the actuator applying a small controlled contact closing pressure.

It is another object to provide a combined elastic diaphragm switch actuator which is fast enough to reliably 3,5 17,149 Patented June 23, 1970 detent an interposer element but which applies a contact closing pressure at a relatively slow rate.

A further object is to provide a multiple circuit diaphragm type switch with independent circuit closing actuators each normally held in an inactive position by an interposer but releasable to drive a member having a controlled rate of force transmission to close its associated circuit and with each released element holding its interposer in an operated position.

The foregoing and other objects, features and advantages of the invention will be apparent from the. following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings.

Drawings In the drawings:

FIG. 1 is a plan view of a multiple circuit switch as described herein;

FIG. 2 is a side view of the switch in a circuit open condition; and

FIG. 3 is a view similar to FIG. 2 but with the parts in an interposer latched condition.

Detailed description The switch actuators are described as embodied in an alpha-numeric transmission terminal having a typewriter type keyboard. In such a terminal, there would be, see FIG. 1, a switch supporting frame 10 extending across the machine and supporting a plurality of interposers 11. There will normally be one interposer 11 for each key of the keyboard. A multi-circuit switch 12 having at least one circuit for each interposer is mounted on the top surface of frame 10 with the circuits of switch 12 in alignment with the interposers 11. Switch 12 will usually be constructed of a bottom substrate 13 having printed circuit type contacts and wiring 14 thereon. This is partially covered by a pair of sheets of a plastic insulating material such as Mylar a lower sheet 15 having perforations at the contact points on substrate .13 and an upper sheet 16 having thin flexible circuits printed thereon to form the other switch contacts and connecting circuits. Parts 13, 15 and 16 are held in place by a rigid retainer plate, not shown. A spring support is mounted by screws 17 to the top surface of switch 12 and comprises a lower bar 18, an intermediate bar 19 having an inclined upper surface and an upper bar 20 having a matching inclined lower surface. A sheet of spring material is clamped between bars 18 and 19 and is slotted at its right extension to provide an actuator finger 21 for each set of contact points of switch 12. Each finger 21 has a small button 22 formed of an elastomeric material and in position to close a set of contacts of switch 12. Each finger 21 has its right end bent upward to form an operating car 23 and the finger will, in its unstressed position, rest with button 22 very slightly, e.g. up to about six mils, above the surface of sheet 16 of switch 12. A second sheet of spring material is clamped between the middle and upper bars 19 and 20 and is also slotted at its forward (right in FIG. 1) side to form spring fingers 24 each lying over a finger 21. Due to the inclined faces of bars 19 and 20, the fingers 24 are angled downwardly at the front but are normally held in an upper, stressed position above cars 23 by the upper ends of interposer 11.

I In operation, depression of a key of the terminal keyboard will rock the upper end of an interposer 11 to the right from the FIG. 2 position to the FIG. 3 position. This will free the right end of the associated finger 24 which will thereon snap behind the interposer 11 and A trademark of the Du Pont Corporation.

hold it in the actuated position of FIG. 3. The downward movement of finger 24 will be very fast and will be limited by its engagement with a stop bar 25 on the upper front edge of frame 10. During a subsequent mechanical operation of the terminal initiated in response to the key operation, the interposer .11 will be depressed until it is below the right end of finger 24 and will then move under the finger. When the interposer 11 is restored to its initial position it will return its spring finger 24 to the ineffective position of FIG. 2.

The downward movement of a finger 24 when released by its interposer 11 will also close the associated circuit switch 12. Near the start of its motion, finger 24 will contact the ear 23 of its aligned finger 21 and move it down until finger 24 impacts stop bar 25. This will press button 22 against the upper film 16 of switch 12 to close its associated set of contacts. The compressibility of button 22 will allow the button to deform so as to spread the applied force over a substantial area of film 16 and thereby reduce stress concentration. The contacts of the switch 12 will initially meet at a central area with a comparatively high pressure which will be useful in breaking through any contaminant film, and due to the deforming of the button 22, the meeting area will enlarge with a slight rolling action of the upper contact over the lower area. At the full depression of finger 21, its button 22 will have deformed sufficiently to wedge the upper diaphragm 16 with its contact into the hole of the lower sheet 15, thereby pressing the contacts into engagement over a sufficient area. To limit both the static and dynamic forces which can be applied through button 22 to film 16, spring finger 2.1 is made of thin flexible spring material and is so designed that after a predetermined static force is transmitted, the finger 21 will tend to pivot about button 22 and will assume a double curvature in the part between button 22 and bars 18 and 19 and thus tend to compensate for any movement of ear 23 after the switch contacts are closed. The stop bar 25 intercepts upper finger 24 before it moves far enough to apply pressure to finger 21 at any point other than on ear 23, limits the deflection of ear 23, and limits the static force applied to the switch.

More importantly, the spring finger 21 has a slow rate of application of dynamic forces so that the energy of the sharp impact of spring finger 24 on ear 23 is applied through the spring 21 and button 22 to the switch diaphragm 16 over a comparatively long interval. This interval gives the diaphragm 16 and button 22 time to yield to the transmitted force and eliminates rupture of the diaphragm.

It may thus be seen that the switch actuator as described herein enables the elastic diaphragm switch to be simplified by elimination of a protective elastomeric film. The actuator also limits the force applied to the switch for contact closure without restriction on the spring force available for the other functions as detenting, etc.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. An actuator for an elastic diaphragm switch having a substrate with contacts thereon, a perforated insulating film covering the substrate and a deformable insulating film on the other side of said perforated film and having flexible conductors pressable through the perforations of said film into engagement with the contacts on said substrate, said actuator comprising a weak spring, a button of an elastomeric compound on said weak spring in alignment with a perforation of said insulating film and, in the unstressed condition of said week spring, closely adjacent to the outer surface of said deformable film, a strong spring which when free will snap into contact with said weak spring to move said button to close an associated pair of contacts of said switch, a moveable interposer normally holding said strong spring clear of said weak spring and a stop bar to arrest said strong spring after it has moved said weak spring and button sufficiently far to close said associated contacts.

2. A switch actuator as in claim 1 in which said weak spring has its free end bent away from said switch to form an ear for contact by said strong spring and in which said strong spring is mounted with its free end inclined toward said weak spring.

3. A switch actuator as in claim 2 in which said button is initially brought into contact with said deformable insulating film to first engage the contacts of said switch over a central area and with substantial pressure and thereafter deforms to engage further areas of said contacts with a slight rolling action and will finally wedge said deformable film into the underlying perforation.

References Cited UNITED STATES PATENTS 1/ 1969 Shlesinger ZOO-67 HERMAN o. JONES, Primary Examiner U.S. Cl. X.R. 200153 

